migrate settings of XPCOM Add-on to WebExtension

Andrew McKay amckay at mozilla.com
Wed Aug 2 15:53:02 UTC 2017

Making an embedded WebExtension as an intermediary step so you can
copy the data across is the recommended way. Here's a blog post that
might help:


There is currently no plan to remove obsolete extensions entries right
now, it might make sense at some point in the future, although people
might still be using them on Nightly. Perhaps once the SDK has been
removed we can consider it, but the risk of serious data loss might
outweigh the benefits for most users.

On 2 August 2017 at 05:20,  <sjw at gmx.ch> wrote:
> Hi there
> What is the easiest way to migrate settings of a pure XPCOM Add-on
> (*not* an embedded WebExtension) to WebExtension? Since they can't
> access each others storage directly this will be hard to implement in a
> user friendly (no action) way.
> And is there a way to remove all obsolete entries from prefs.js during
> the migration? Or will Mozilla clean up the obsolete extensions.*
> entries at some point in the future?
> Some extensions have blown up my prefs.js up to some megabytes which is
> obviously bad for performance reasons.
> Reagrds,
> Jonas
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